The invention relates to a tumbler lock consisting of an outer cylinder having two longitudinal recesses staggered by 180.degree., with an inner cylinder rotatably mounted in the outer cylinder, with at least two springless plate-type tumblers which move freely in guide slots, the tumblers engaging, in the locked state, in one of the longitudinal recesses of the outer cylinder, thus preventing the inner cylinder from rotating. The tumblers are provided with key windows and, during the insertion of the corresponding key, move, positively controlled, in both directions of motion through the key profile from the area of the longitudinal recess to the area of the inner cylinder so that the inner cylinder can rotate to the unlocked position.
When the key is being withdrawn, tumbler locks of known construction with plate-type tumblers are locked because the tumblers engage in a longitudinal recess of the outer cylinder either by the biasing force of a spring or by gravity. The inner cylinder is thus prevented from rotating. All tumblers are locked on the bottom of the longitudinal recess and are therefore on the same level.
Such a tumbler lock can be opened with relative ease by unauthorized persons by inserting an object through the windows in the plate-type tumblers, which are wedged on the side faces of the windows. All the tumblers located in the same plane can be lifted off the longitudinal recess until they come to rest within the dimensions of the rotatable inner cylinder, so that the inner cylinder can be turned. Means for carrying out this procedure are known, and, thus, these types of locks only offer limited safety. Particularly in locks in which the tumblers are not spring-loaded, this procedure can be easily applied because of the free movability of the plates.
More expensively designed locks are known in which the above-mentioned disadvantage can be overcome by plunging the spring-loaded tumbler plates into the longitudinal recess at different depths using stops and projections or lugs. When all the tumblers are lifted together, some of them will engage in the upper or lower longitudinal recesses in the outer cylinder, preventing the lock from opening. Although this measure prevents the lock from easily being opened by lifting all the tumblers, it does not rule out the possibilty of tracing the locking edges on the individual tumblers. Thus, a burglar equipped with the known and necessary tool has no difficulty opening such a lock.
The inner cylinder must be rotated as the locking edges are being traced, so that the tumblers rub with their locking edges in the guide slots. The locking edges can then be traced during the lifting of the tumblers. Locks are known which render this tracing difficult. For this purpose, the tumblers and, accordingly, the longitudinal recess in the outer cylinder of the lock in which the tumblers engage in the closed state, are provided with profiles and hookings to prevent the inner cylinder from rotating easily. This measure renders unauthorized opening of the lock more difficult. However, since there is the possibility of manipulating objects, which are inserted in the key channel, directly on the tumblers, it is only a question of time and skill to open such a lock.